Transport of angular momentum by stochastically excited waves as an explanation for the outburst of the rapidly rotating Be star HD49330

Abstract

HD49330 is a Be star that underwent an outburst during its five-month observation with the CoRoT satellite. An analysis of its light curve revealed several independent p and g pulsation modes, in addition to showing that the amplitude of the modes is directly correlated with the outburst. We modelled the results obtained with CoRoT. We modelled the flattening of the structure of the star due to rapid rotation in two ways: Chandrasekhar-Milne's expansion and 2D structure computed with ROTORC. We then modelled kappa-driven pulsations. We also adapted the formalism of the excitation and amplitude of stochastically excited gravito-inertial modes to rapidly rotating stars, and we modelled those pulsations as well. We find that while pulsation p modes are excited by the kappa mechanism, the observed g modes are a result of stochastic excitation. In contrast, g and r waves are stochastically excited in the convective core and transport angular momentum to the surface, increasing its rotation rate. This destabilises the external layers of the star, which then emits transient stochastically excited g waves. These transient waves produce most of the low-frequency signal detected in the CoRoT data and ignite the outburst. During this unstable phase, p modes disappear at the surface because their cavity is broken. Following the outburst and ejection of the surface layer, relaxation occurs, making the transient g waves disappear and p modes reappear. This work includes the first coherent model of stochastically excited gravito-inertial pulsation modes in a rapidly rotating Be star. It provides an explanation for the correlation between the variation in the amplitude of frequencies detected in the CoRoT data and the occurrence of an outburst. This scenario could apply to other pulsating Be stars, providing an explanation to the long-standing questions surrounding Be outbursts and disks.

arXiv commentAccepted in A&A, 15 pages, abstract shown here has been abridged to fit Arxiv's character limit

References in corpus (29)

• The CoRoT satellite in flight : description and performance
• Classical Be Stars: Rapidly Rotating B Stars with Viscous Keplerian Decretion Disks
• Sub-surface convection zones in hot massive stars and their observable consequences
• Effects of gravitational darkening on the determination of fundamental parameters in fast rotating B-type stars
• Internal Gravity Waves in Massive Stars: Angular Momentum Transport
• Nonlinear mode coupling in rotating stars and the r-mode instability in neutron stars
• Simulations of core convection in rotating A-type stars: Differential rotation and overshooting
• Excitation of stellar p-modes by turbulent convection: 1. Theoretical formulation
• Theory and evidence of global Rossby waves in upper main-sequence stars: r-mode oscillations in many Kepler stars
• Three-Dimensional Simulations of Massive Stars: I. Wave Generation and Propagation
• The Magnetic Furnace: Intense Core Dynamos in B-stars
• On the Differential Rotation of Massive Main Sequence Stars
• Rotating helical turbulence. Part I. Global evolution and spectral behavior
• Theoretical seismology in 3D : nonlinear simulations of internal gravity waves in solar-like stars
• Gravity modes in rapidly rotating stars. Limits of perturbative methods
• Numerical 3D constraints on convective eddy time-correlations : consequences for stochastic excitation of solar p modes
• Stochastic excitation of non-radial modes I. High-angular-degree p modes
• Generation of internal gravity waves by penetrative convection
• Impact of rotation on stochastic excitation of gravity and gravito-inertial waves in stars
• A model of rotating convection in stellar and planetary interiors: I - convective penetration
• Angular momentum transport by internal gravity waves III - Wave excitation by core convection and the Coriolis effect
• Solar-like oscillations in massive main-sequence stars. I. Asteroseismic signatures of the driving and damping regions
• Angular momentum transport by stochastically excited oscillations in rapidly rotating massive stars
• R modes of slowly pulsating B stars
• A model of rotating convection in stellar and planetary interiors: II -- gravito-inertial wave generation
• Amplitudes of low frequency modes in rotating B type stars
• The Traditional Approximation of Rotation including the centrifugal acceleration for slightly deformed stars
• Mode excitation by turbulent convection in rotating stars. I. Effect of uniform rotation
• Entropy and energy spectra in low-Prandtl-number convection with rotation

Cited by in corpus (24)

• Probing the interior physics of stars through asteroseismology
• On the Origin of Stochastic, Low-Frequency Photometric Variability in Massive Stars
• An all-sky sample of intermediate- to high-mass OBA-type eclipsing binaries observed by TESS
• Detection of nonlinear resonances among gravity modes of slowly pulsating B stars: results from five iterative prewhitening strategies
• Asteroseismology of the young open cluster NGC 2516 I: Photometric and spectroscopic observations
• Asteroseismic g-mode period spacings in strongly magnetic rotating stars
• Seismic modeling of a very young SPB star -- KIC8264293
• Rossby numbers and stiffness values inferred from gravity-mode asteroseismology of rotating F- and B-type dwarfs: consequences for mixing, transport, magnetism, and convective penetration
• Overstable Convective Modes in Rotating Early Type Stars
• TESS observations of Be stars: general characteristics and the impulsive magnetic rotator model
• Ultraviolet Spectropolarimetry: on the origin of rapidly rotating B stars
• The traditional approximation of rotation for rapidly rotating stars and planets. I. The impact of strong deformation
• Short-term variability and mass loss in Be stars VI. Frequency groups in $\gamma$ Cas detected by TESS
• Stochastic excitation of internal gravity waves in rotating late F-type stars: A 3D simulation approach
• Be star discs: powered by a non-zero central torque
• Space Photometry with BRITE-Constellation
• Effect of Rotation on Wave Mixing in Intermediate Mass Stars
• Nonlinear internal waves breaking in stellar radiation zones. Parametrisation for the transport of angular momentum: bridging geophysical to stellar fluid dynamics
• 3D MHD Simulation of a Pulsationally-Driven MRI Decretion Disc
• The impact of rotation on the stochastic excitation of stellar acoustic modes in solar-like pulsators
• A TESS search for donor-star pulsations in High-Mass X-ray Binaries
• Asteroseismology
• Towards a systematic treatment of observational uncertainties in forward asteroseismic modelling of gravity-mode pulsators
• Binarity at LOw Metallicity (BLOeM): massive star variability revealed using a novel software tool for point-spread function fitting of TESS images